An equipment or a device is configured such that plural members are jointed together. Examples of such joining include mechanical joining such as using a bolt, as well as adhesive bonding, welding, diffusion bonding, and room temperature bonding. Adhesive bonding needs an inclusion such as glue and brazing material, while welding and diffusion bonding need high-temperature heating.
In contrast, room temperature bonding is that which utilizes atomic force (surface energy) possessed intrinsically by surface atoms of members to be bonded and which is performed within a ordinary temperature range (from room temperature to low temperature range). According to the room temperature bonding, strong bonding can be allowed even by a small input energy, so that large heat strain and structural change will be prevented from occurring in the vicinity of the junction interface.
The room temperature bonding occurs when atoms (surface atoms) that constitute surfaces to be bonded (bonding surfaces) of members to be bonded are exposed and close to one another and if attractive force (atomic force) acting between their surface atoms exceeds an internal stress that acts in the opposite direction. Accordingly, the conventional room temperature bonding is performed such that bonding surfaces having good surface roughness and flatness are contacted with each other in a state where films such as oxide films and adsorption films of organic substances have been removed.
More specifically, friction welding and narrowly-defined ultrasonic bonding, etc. are industrially performed. In such cases, mechanical friction removes films such as oxidation films on the bonding surfaces to result in room temperature bonding with assistance by the activation of the surface atoms due to friction heat. In this room temperature bonding, the temperature does not rise to the melting point, but the vicinity of the bonding interface is heated to some extent, so that heat strain and structural change, etc. are likely to occur. In addition, the shape and other features of the jointed members may be restricted because the bonding surfaces must be subjected to ultrasonic vibration while being pressurized together at a high pressure to be bonded.
Other than using the mechanical friction, Patent Literature (PTL) 1 or PTL 2 below and other literature propose a room temperature bonding method in which inert gas beam and/or plasma, etc. are irradiated to bonding surfaces to remove films such as oxidation films on the junction surfaces (pretreatment), and the bonding surfaces are thereafter bonded together in vacuum. In addition, PTL 3 proposes forming hardly-oxidizable thin films of gold (Au) on the bonding surfaces and thereafter promptly performing room temperature bonding in the air.